Evaluate if x=7 and y=3.

x²-7xy
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4

In mathematics, an algebraic expression is an expression built up from integer constants, variables, and the algebraic operations. For example, 3x² − 2xy + c is an algebraic expression. Since taking the square root is the same as raising to the power 1/2, {\sqrt {\frac {1-x^{2}}{1+x^{2 is also an algebraic expression. By contrast, transcendental numbers like π and e are not algebraic, since they are not derived from integer constants and algebraic operations. Usually, Pi is constructed as a geometric relationship, and the definition of e requires an infinite number of algebraic operations. A rational expression is an expression that may be rewritten to a rational fraction by using the properties of the arithmetic operations. In other words, a rational expression is an expression which may be constructed from the variables and the constants by using only the four operations of arithmetic. Thus, {\frac {3x^{2}-2xy+c}{y^{3}-1}} is a rational expression, whereas {\sqrt {\frac {1-x^{2}}{1+x^{2 is not. A rational equation is an equation in which two rational fractions of the form {\frac {P(x)}{Q(x)}} are set equal to each other.

From a fifth grader

21 is the answer the answer is 21